Array.prototype.random = function(length) {
  return this[Math.floor(Math.random() * length)];
};

var country = [{
    name: "romaniei",
    capital: "bucuresti"
  }, {
    name: "bulgariei",
    capital: "sofia"
  }],
  questions = [
    "What is the capital of ",
    " is the capital of what country?"
  ]

document.querySelector('input').onclick = function() {
  var q,
    chosen_country = country.random(country.length),
    chosen_question = questions.random(questions.length);

  if (chosen_question == questions[0]) {
    q = chosen_question + chosen_country.name + "?";
  } else if (chosen_question == questions[1]) {
    q = …